Miliband, the former Labour leader, was the first ever Secretary of State for Energy and Climate Change when Gordon Brown created the department in 2008.

Asked if climate change issues had been downgraded, a spokesperson for the prime minister said the government “will be continuing to meet our international commitments.”

No.10 added: “It makes sense that the areas around business and industrial strategy should be linked up with energy. So that is a department that will be created with energy at the heart of it.”

Lisa Nandy, who served as Jeremy Corbyn’s shadow DECC secretary until she resigned last month, told The Huffington Post UK: “It is now within the gift of Theresa May and Greg Clark to choose whether the UK will remain a global leader on climate change or abandon the decades long commitment that began with the creation of DECC and the passage of the Climate Change Act.

“They must throw the power of this new Department behind building a cleaner economy.”

Dan Kitwood via Getty Images

Barry Gardiner, who had shadowed the old department for Jeremy Corbyn, told HuffPostUK: “We must see this decision in the context of other actions taken by the government.

“They axed a world-leading competition for Carbon Capture and Storage, pulling the rug out from under investors at the last minute.

“They cut all support for the cheapest form of clean energy in onshore wind. They have left a black-hole for clean energy investment beyond 2021, providing no certainty for business.

“Since the referendum they have talked up their commitment to our climate obligations. But in fact this government is downgrading action on climate change. The rhetoric is positive, the actions are overwhelmingly negative.”

Anthony Devlin/PA Wire
Caroline Lucas

Green MP Caroline Lucas said the decision to shut down DECC was “a deeply worrying move from Theresa May”.

“Climate change is the biggest challenge we face, and it must not be an afterthought for the Government,” she said.

“Dealing with climate change requires a dedicated Minister at the Cabinet table. To throw it into the basement of another Whitehall department looks like a serious backwards step.

“In the coming months I will work constructively with any Minister willing to take climate change seriously, and I’ll be holding the Government to account for any backpeddling on our climate change commitments.”

The decision to shut DECC was also criticised by the The Institute For Public Policy Research (IPPR) think-tank as it risked “reversing ten years of progress on reducing the threat of global warming”.

Michael Jacobs, IPPR Acting Associate Director for Energy, Transport and Climate said: “If it is to be a success, its new focus on industrial strategy must be low-carbon. Greg Clark needs to move swiftly to reassure energy investors that there will be no change in the commitment to decarbonisation and that the Chancellor’s Autumn Statement will provide the policy framework to restart investment in vital low-carbon infrastructure.”

Following his appointment, Clarke said: “I am thrilled to have been appointed to lead this new department charged with delivering a comprehensive industrial strategy, leading Government’s relationship with business, furthering our world-class science base, delivering affordable, clean energy and tackling climate change.”